1. Field of the Invention
The present invention relates generally to an apparatus and a method for encoding and decoding in a portable terminal. More particularly, the present invention relates to an apparatus and a method for enhancing a coding efficiency in a portable terminal which adopts a bandwidth extension.
2. Description of the Related Art
With advances in digital signal processing technology, audio signals are typically stored and reproduced as digital data. A digital audio storing/reproducing apparatus samples and quantizes an analog audio signal, converts the analog signal into a digital audio data using Pulse Code Modulation (PCM), and stores the digital data to an information storage medium such as Compact Disc (CD) or Digital Versatile Disc (DVD). Because the data is conveniently stored, a user may reproduce the audio data on demand.
In comparison to other methods, the digital method provides an enhanced sound quality. For example, compared to a method which estimates and restores a high band signal from a low band signal or a feature vector extracted from the low band signal that reproduces only the low band signal at the receiver using an artificial BandWidth Extension (BWE), the sound quality of the digital method is enhanced.
As an example of a receiver using BWE, provided that a sampling frequency Fs of an input signal is 16 kHz, the bandwidth extension restores the high band signal of 4 k˜8 kHz from the low band signal of 0˜4 kHz and produces the same signal 16 kHz as the original input signal. The success of the bandwidth extension is closely related with a correlation between the frequency bands (the high band and the low band) of the input signal.
When the input signal of one frame is divided into the low band and the high band based on the frequency band, the signals of the two bands have a close correlation because they are generated from the same source. If the correlation or mutual information between the two bands is considerable, the high band signal recovered through the bandwidth extension exhibits sound quality that is close to the original sound.
However, when there is only a small amount of information relating to the high band signal because of a low correlation between the two bands, the bandwidth extension cannot adequately restore the high band signal.
Accordingly, there is a need for an improved apparatus and a method for enhancing performance of a coding apparatus using a bandwidth extension in a portable terminal.